Combination of pulsed digital holography and laser vibrometry for the 3D measurements of vibrating objects

An optoelectronic system is presented that is used to measure the three dimensional vector components of a vibrating object. The complete determination of the vibration occurs by combination of three different measurements. 1). A 3D system based on digital holography for the measurement of the three dimensional deformation vector along the directions x, y and z is used. Pulses from a ruby laser, with a separation in the range from 1 to 1000 microseconds, are used to record holograms on CCD sensors, which are later digitally reconstructed. 2). The shape of the object is determined. In this case too the ruby laser is used as a light source but now two pulses are emitted with different wavelengths. The wavelength change is produced by changing the distance between the plates of the laser output etalon. The shape is obtained by subtraction of the phases of the wavefronts recorded at the two different wavelengths. 3). For the absolute measurement of a vibration using double exposure holographic techniques, it is necessary to have a reference point where the absolute vibration is known. A precise measurement of the vibrations in a point is done by using a 3D laser Doppler vibrometer.